Twisting and warping of rigid polyvinyl chloride plastic rec

The air duct machine is uneven in appearance, the diagonal line is not flat, the adjacent surfaces are not vertical to each other, and the two pipe ends are not parallel in plane.

2. Cause analysis

(1) In the process of opening and cutting, the four sides of rectangular sheet metal are not strictly angled.

(2) The length and width of the two opposite sides of the duct are not equal.

(3) No heating folding.

(4) The groove of plastic welding is incorrect.

3. Prevention and control measures

(1) Hard polyvinyl chloride plastic sheet is made by laminating method. After being heated again in the process of making air duct machine, because there are anisotropy and residual stress in the lattice, it will shorten after cooling. Therefore, before cutting, it is necessary to do experiments on the reduction of each batch of sheets. After determining the value of reduction in practice, the shortened part should be released before cutting. When marking and cutting the sheet, it should be the same as the metal air duct, and use angle ruler to corner the four corners of the sheet.

(2) It is necessary to ensure that the length and width of the two opposite edges are equal, and the two pieces of material are overlapped to check the scale.

(3) Rectangular air duct made of rigid polyvinyl chloride plastic sheet. In order to ensure the strength of air duct, the welding seam is not located at four edges and corners. Four edges and corners should be folded by plastic plate and tube electric heater. When folding, we should put the Striped plate in two tube electric heaters, and align the folded line to the heater, so that the part of the folded line is heated. After softening the heating place, the plate is pulled out and placed on the edge machine or folding machine. The plate is folded into a 90 degree angle. After cooling and setting at the heating place, the plate can be removed.

(4) When welding rigid PVC plastic sheets, in order to make the sheets well combined and have high welding strength, the edge of the sheet should be grooved, and the viewpoint and scale of the groove should be uniform.